1. Technical Field
The present invention relates to a radio communication terminal and a method of controlling internal radio communication, and in particular, it relates to a control method applicable to a clamshell cellular telephone.
2. Background Art
Liquid crystal displays mounted in recent cellular telephones are provided with higher resolution to display still images such as characters and graphics and also still images and moving images picked up by digital cameras at higher definition. With this, the amount of data exchanged between digital cameras and liquid crystal displays is increasing, and it is proposed in Japanese Patent No. 3,086,456 that a high-speed transfer mode called low voltage differential signaling (LVDS) be used to connect displays and image photographing devices.
Also, recent cellular telephones adopt a clamshell structure in which the cellular telephones can be folded to increase the size of the displays without losing portability and prevent unintended pushing of operation buttons when they are being carried. In the clamshell structure, a first casing housing a control panel that principally controls the external radio communication of a cellular telephone and a second casing housing a display are connected together with a hinge, and the first casing and the second casing can be closed and opened via the hinge.
Also, in order to allow a weak GPS signal to be received even while transmitting from a moving platform, JP-T-2003-507954 for example discloses a method in which a branch unit is provided upstream from the antenna for branching part of the transmitted signal, an interference compensating signal is taken out by attenuating and phase-shifting the signal branched by the branch unit, and the interference compensation signal is superimposed on the GPS signal.
However, as the display mounted on a cellular telephone comes to have higher resolution, to transmit high-bit-rate image data by wire, it is necessary to provide the flexible wiring board for transmitting the signal to the display with a multipin structure. Accordingly, when data transmission between the first casing and the second casing is performed by wire in a cellular telephone with the clamshell structure, it is necessary to pass the multipin flexible wiring board through the hinge, complicating the hinge structure and the mounting process. As a result, this presents an obstacle to more compact and thinner cellular telephones, increases cost, and decreases reliability.
On the other hand, when an internal radio communication antenna is provided to both the first casing and the second casing in place of the flexible wiring board, in which data transmission between the first casing and the second casing is performed by internal radio communication, interference is generated between it and the external radio communication of the cellular telephone. This poses the problem of changing the environment of the internal radio communication depending on the status of the external radio communication, so that the reliability of data transmission is not decreased.
Particularly, when a radio communication system in which output is limited to a low level, such as an ultra wide band (UWB) system, is adopted for the internal radio communication, the difference in power level between it and a radio wave outputted in the external radio communication of the cellular telephone is large, such as 90 dB. This also presents the problem that the influence of signals outside the specific frequency band of the internal radio communication cannot be ignored, there being deterioration of the radio communication environment due to the interference of the external radio communication of the cellular telephone which increases the bit error rate and packet error rate leading to an increase in the need for retransmissions.
Also, even when a radio communication system in which only weak power is radiated is adopted, those radio waves interfere with the cellular telephone system because the latter requires high reception sensitivity, posing the problem that the reception sensitivity of the cellular telephone system is decreased.
Also, the method disclosed in JP-T-2003-507954 requires a branch unit, an attenuator, a phase shifter, and a superimposer. This produces the problem of complicating the circuit structure and increasing the size, resulting in an increase in cost, size, and weight.
Accordingly, it is an object of the present invention to provide a radio communication terminal and a method of controlling internal radio communication capable of preventing the deterioration in the quality of internal radio communication between the first casing and the second casing, by allowing for a change in the state of external radio communication.